The cases we have documented since then using the revised federal baseline reaffirm our major findings. The horrific massacre at a movie theater in Aurora, Colorado, in July 2012, another at a Sikh temple in Wisconsin that August, another at a manufacturer in Minneapolis that September—and then the unthinkable nightmare at a Connecticut elementary school that December—were some of the latest in an epidemic of such gun violence over the last three-plus decades.

Since then, we’ve updated and expanded it multiple times with additional research and reporting.The analysis and charts above cover the data through 2012 (comprising 62 cases); additional data and analysis on the shooters’ weapons are in this story.A recent analysis of this database by researchers at Harvard University, further corroborated by a recent FBI study, determined that mass shootings have been on the rise.We’ve gathered detailed data on more than three decades of cases and mapped them below, including information on the attackers’ profiles, the types of weapons they used, and the number of victims they injured and killed.While those larger datasets of multiple-victim shootings may be useful for studying the broader problem of gun violence, our investigation provides an in-depth look at the distinct phenomenon of mass shootings—from the firearms used to mental health factors and the growing copycat problem.

Tracking mass shootings is complex; we believe ours is the most useful approach.We exclude shootings stemming from more conventional crimes such as armed robbery or gang violence.Other news outlets and researchers have published larger tallies that include a wide range of gun crimes in which four or more people have been either wounded or killed.The interactive map below and our downloadable database have been expanded with 33 additional cases from 2013-2017.Dating back to at least 2005, the FBI and leading criminologists essentially defined a mass shooting as a single attack in a public place in which four or more victims were killed.And: Explore the full data set behind our investigation.